/*
 * Copyright (c) 2006 Your Corporation. All Rights Reserved.
 */

/**
 * Copyright 2007 Jason Horman, Pete Aykroyd
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.functor.expression;

import org.apache.commons.lang.ObjectUtils;

public abstract class AbstractExpression implements Expression, Comparable {
	private transient int cachedHashCode = -1;
	private transient String cachedToString;

	public final String toString() {
		if (cachedToString == null) {
			StringBuilder builder = new StringBuilder();
			toString(builder);
			cachedToString = builder.toString();
		}

		return cachedToString;
	}

	protected abstract void toString(StringBuilder builder);

	public boolean equals(Object o) {
		return ObjectUtils.equals(toString(), String.valueOf(o));
	}

	public final int hashCode() {
		if (cachedHashCode == -1)
			cachedHashCode = computeHashCode();
		return cachedHashCode;
	}

	public int computeHashCode() {
		return toString().hashCode();
	}

	public int compareTo(Object o) {
		return toString().compareTo(String.valueOf(o));
	}

	public void modified() {
		cachedHashCode = -1;
		cachedToString = null;
	}
}
